Multielement electron discharge apparatus and system



April 25, 1939. R. A. HEIS ING 2,156,088

MULTIELEMENT ELECTRON DISCHARGE APPARATUS AND SYSTEM FiledJan. 11, 19363 Sheets-Sheet l INVENTOR R. A. HE ISING ATTORNEY April 25, 1939. IHE|$|NG 2,156,088

MULTIELEMENT ELECTRON DISCHARGE APPARATUS AND SYSTEM Filed Jan. 11, 19363 Sheets-Sheet 3 F/G. I 77 87 f T 7 4 l8 I. aa

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ATTORNEY Patented Apr. 25, 1939 UNITED STATES PATENT OFFICE Raymond A.Heising, Bell Telephone New York, N. Y., a

Summit, N. J., assignor to boratories, corporation of New YorkIncorporated,

Application January 11, 1936, Serial No. 58,653

17 Claims.

This invention relates to electron discharge systems and moreparticularly to circuits employing electron discharge devices tosimultaneously perform a number of different functions.

The various functions for which electron discharge tubes have been usedsuch as generation of oscillations, production of harmonics of theoscillations, modulation of oscillations in accordance with signal orcontrol waves and amplification of oscillations have generally beenperformed by individual discharge devices. This is for the reason thatthe requirements imposed upon the device and its associated circuits byone function are frequently unfavorable to the performance of some otherfunction. Moreover, it has been highly desirable to be able to secureindependence in the control or adjustment of one of the functions sothat each operation may be performed most efficiently and undisturbed byadjustments required to establish the proper conditions for anotheroperation.

The generation of oscillations and the modulation of the generatedoscillations in accordance with message or control waves for carrierWave transmission as is ordinarily required in carrier line transmittersor radio transmitters is an example of two fequently associatedfunctions which present an opportunity for the use of multifunction tubecircuits. Coupled frequently with these two functions is that ofsuppressing any unmodulated carrier wave component so that only theside-bands produced by the modulating operation or the pure modulatedwave may be transmitted. Corresponding situations occur in carrier wavereceiving systems and particularly in those of the heterodyne orsuperheterodyne types where it is frequently necessary to generate localoscillations and to combine them with incoming or received oscillationsin a device which does not permit tuning of either the primary receivingcircuit or of the local oscillator frequency determining circuit tointerfere with or react upon the other.

According to the invention an electron discharge device is provided withthree electrodes corresponding to the usual cathode, grid and anode andeach electrode is so polarized and the external grid and anode circuitsare so coupled as to cause oscillations to be generated. The anodediffers from that of the usual type in that it is of foraminate orscreen type so that a portion of the electrons emitted from the cathodeand impelled by the positive anode potential in the direction of theanode are not intercepted by the anode but pass into the space beyond.Additional systems of electrodes in the same envelope operate upon theseelectrons in the region beyond the oscillator anode to imposemodulations or control characteristics upon the stream which theelectrons constitute in addition to the pulsation which it alreadypossesses by virtue of the oscillating potentials on the oscillator gridand anode. If one of the additional electrodes beyond the oscillatoranode be given a normal negative polarization, its potential may be sopredetermined if desired as to retard the electrons which pass the anodeand toreduce their velocity substantially to zero at some plane orregion beyond the anode. Subsequent courses of these electrons dependupon the electrical environment of the Zero velocity plane or region,which has been called a virtual cathode for the reason that in theirsubsequent transit the electrons may be regarded as having beenoriginally emitted at the locus of the virtual cathode.

The pulsating electron stream which passes beyond the transmitteroscillator anode may be directed toward a pair of additional electrodeseach of which absorbs its portion of, the electrons. By impressingmodulating potentials between the anodes the relative portions of thepulsating electron stream which they absorb may be varied in accordancewith the modulating forces. Accordingly, an output or work circuitdiiferentially connected to the additional anodes will receive no energyas long as the modulating fosces are zero but will receive pulsations ofthe oscillator frequency corresponding to the difference in the twoanode streams during modulation. Since these modulated pulsations arefree from the normal unmodulated component the output Wave will be ofthe well-known suppressed carrier type. A similar effect may be obtainedif in lieu of applying the modulating electromotive forces between theadditional anodes, it is applied between a pair of additional grids sopositioned that each lies in the path of the main electron stream fromthe virtual cathode to one of the additional anodes. The additionalgrids alternately accelerate and impede their individual electronstreams thus in effect switching the main stream to greater or lessextent from one of the additional anodes to the other.

In the drawings:

Fig. 1 discloses a single tube circuit which serves as a combinedoscillator and balanced modulator; Fig. 2, a modification in which themodulating grids serve also as screens for the modulator anodes at highfrequencies; Fig. 3, a

modification of the circuit of Fig. 2 in which separate shielding isemployed; Fig. .4, a simplified apparatus in which the two modulatorgrids serve as parallel connected anodes for the oscillator; Fig. 5, afurther simplification which is the equivalent of two three-electrodetubes connected in parallel for oscillation and in push pull formodulation; Fig. 6, modification of the circuit of Fig. 4; .Fig. 7, aplate modulation circuit; Fig. 8, a device in which a virtual cathodesupplies a speech modulated electron stream for the space current pathof an oscillator; Fig. 9, a signal modulated virtual cathode apparatusto supply the electron stream of a modulator; Fig. 10, harmonicgenerator circuit employing multiple electrode tubes; Figs. 11 and 12,two different harmonic generator circuits in which the primary or basefrequency oscillator elements are arranged in push-pull fashion; Fig.13, a circuit for producing harmonics from a crystal-controlledgenerator, and Fig. 14, a circuit of a crystal-controlled oscillator forsupplying high power oscillations to a load circuit.

Referring to Fig. 1 an electron discharge device I of the highlyevacuated type contains a thermionic cathode 2, an oscillator grid 3,and a foraminate oscillator anode 4. A virtual cathode 5 represented bya line of dots is established by negatively biased modulator grids 6 andI which tend to retard electrons from cathode 2 impelled through themeshes of anode 3. Modulator anodes 8 and 9 are respectively connectedto the opposite terminals of a capacity element II] which, together withan inductance I I serving as the primary'winding of a transformer,constitutes a tun-ed output circuit. A source I2 of space current isconnected between the cathode 2 and a central point of inductance I I.Grid 3 and anode 4 are connected to the opposite terminals of afrequency-determining tuned circuit I3 the electrical midpoint of whichis connected to a point in the space current source I2. Grid 3 is biasednegatively by grid leak current and anode 4 is positively biased by thespace current source I2. The elements 2, 3 and 4 with their associatedtune circuit 53 and biasing sources constitute an oscillator ofwell-known type.

Grids 6 and I are connected to opposite. terminals of the secondarywinding of a voice fre quency transformer I4 and are polarized to such anegative potential by source I5 that part of the electrons from cathode2 passing through the oscillator anode 4 are substantially brought to astop in the region of the virtual cathode 5. The modulator anodes 8 and9 have such positive potential as to tend to draw the electrons from thevirtual cathode. The grids 6 and 'I are alternately rendered positiveand negative with respect to their own normal negative bias potential bysound signals incident upon microphone I6 in circuit with source I? andthe primary winding of transformer I4. When grid 6 is driven in apositive direction electrons move from the virtual cathode region toplate 8. On the reverse part of the signaling cycle grid I is driven ina positive direction and. electrons move toward plate 9. When there isno signal electromotive force generated and grids 6 and I remain at thesame potential the pulses of electrons passing to anodes 8 and 9 areequal and neutralize in their effect in the primary winding I I and. nooscillations are supplied to output circuit I8.

The circuit of Fig. 1 may also be used for detection purposes if insteadof elements I6, I1 and audio frequency transformer a high frequencyreceiving circuit or antenna associated with a rado frequencytransformer is connected to grids 6 and I. In that case the transformerof which inductance I I forms the primary winding should be so designedas to effectively transmit the detected currents to output circuit I8.

Fig. 2 shows a circuit similar to that of Fig. 1 but without the virtualcathode feature and in which the modulating grids serve also as highfrequency shields for the anodes. As like parts are similarly designatedit will be understood that elements 2, 3, and I3 constitute a highfrequency oscillator the frequency of which is determined by tunedcircuit I3. Anodes 8 and 9, capacity element Ill, inductance II andanode source I2 correspond to the similar elements of Fig, 1. Amicrophone I6. current source I1 and balanced audio frequencytransformer I4 serve to apply low frequency signal electromotive forcesto the grids I9 and I9a. Audio frequency electromotive forces areimpressed on each grid over a path extending from the cathode by way ofthe grid bias source to the midpoint of the. secondary winding oftransformer I4, through the appropriate portion of the secondary windingand the radio-frequency choke coil 20 to the respective grid. The gridbias source is indicated in the drawings as having a polarity toward thegrid which may be either positive or negative. In the usual case thegrids I9 and I9a will be biased positively with respect to the cathode.However in the event that a high output power is desired the anodevoltage will preferably be made high and in order to avoid a power lossin the grid circuit the polarity of the biasing source may be such as torender the grids negative. The grids may also be made negative to avoidpower loss in the grid. circuit in the case where only a medium or lowanode potential is used and in this case the mesh of the grids willpreferably be increased to reduce the decelerating effect of the I gridsupon the electrons. Whenever the grids are biased negatively there is a.tendency to form a virtual cathode and the degree to which such acathode is formed is a function of the magni tude of the negative gridbias potential utilized. Connecting the grids directly to the cathodeare capacity elements 2I which serve to bring the grids to the cathodepotential at high frequencies but which are of too small capacity topermit signal frequency electromotive forces to be shunted thereby.Choke coils 29 prevent the external circuit of grids I9 and I9a fromentering into the high frequency operation in any way. The grids I9 andI9a are of the screen type and as such are designed to serve as shieldsfor the anodes 8 and 9 so that direct interelectrode capacitance effectsbetween anodes 8 and 9 and the remaining electrodes of the tube aresubstantially eliminated. Consequently, the tuned output circuit 22 willnot react upon the oscillator to affect its frequency. As in the circuitof Fig. 1, signal electromotive forces on one-half cycle increase oneelectron stream, e. g., that to the anode Band decrease that to theother and on the reverse half cycle bring about an opposite result. As aresult, anodes 8 and 9 receive pul sating electron streams, theinstantaneous mag nitudes of which, in the absence of signalelectromotive forces in transformer I4, are alike so that the resultantor differential output current supplied to the load circuit under thosecircumstances is zero. When signal electromotive forces occur theresultant high frequency current supplied to the output circuit I8 is apure modulated wave, 1. e., a modulated carrier wave devoid of anyunmodulated component of the carrier frequency.

Fig. 3 shows a circuit that is similar to that of Fig. 2. In thiscircuit the modulating grids 23 and 24 serve solely for modulatingpurposes. To eliminate any interelectrode capacitance effect at theoscillation frequency, the discharge device is provided with two sets ofscreening grids 25 and 26 each of which is connected by a capacityelement 2| constituting a low impedance path at the oscillationfrequency to the cathode. The grid bias source in shunt to each capacityelement 2| is indicated as impressing either positive or negativepotential upon the respective grid. This feature has been explained inconnection with the similar biasing source of Fig. 2. Screen grid 25effectively isolates anodes 8 and 9 and output circuit 22 from theoscillator elements. Screen grid 26 which may be used together with grid25 or as a substitute for it also serves to eliminate interelectrodecapacity effects at high frequencies between the oscillator electrodesand the remaining elements of the discharge device.

In Fig. 4, the functions of the foraminate oscillator anode and themodulating grids are combined with a simplification of the structureinvolved. The oscillator comprises cathode 2, oscillator grid 3 and thetwo foraminate anodes 2! and 28 connected to the oscillationfrequency-determining circuit l3 by parallel paths including blockingcondensers 29 and 30 which permit high frequency oscillations to passbut prevent unidirectional space current sources from impressingpotentials on the oscillator grid 3. The anodes 21 and 28 are connectedto space current source I2 through choke coils 3| and 32 which suppresscurrents of the oscillation frequency but do not seriously impede voicefrequency, or other low frequency modulating currents. Modulatingelectromotive forces are impressed from the secondary winding oftransformer l4 through high frequency choke coils 3| and 32 uponelectrodes 21 and 28 which, although connected in parallel as oscillatoranodes, are connected in push-pull fashion to serve as modulator grids.The effective potentials of electrodes 21 and 28 are thus alternatelyincreased and decreased in turn so that the one electron stream to anode8 is increased as that to anode 9 is decreased and vice versa.Accordingly, load circuit l8 receives a signal modulated oscillationthat is free from any unmodulated component of the carrier frequency.

Fig. 5 illustrates a further simplification in which the same anodes,control electrodes and cathode serve for both the oscillator andmodulater. The cathode 2 is connected to the two oscillator grids 33 and34 by parallel paths extending through capacity elements 29 and 30 whichreadily pass the oscillation frequency currents but are of highimpedance for speech cur-' rents or other low frequency modulatingcurrents. The anodes 8 and 9 are supplied with space current from spacecurrent source over a path extending through radio frequency choke coil35 and the inductance of output circuit 22. Modulation electromotiveforces are impressed from the secondary winding of transformer I4 inpushpull fashion on elements 33 and 34, serving as modulator grids, byway of paths through choke coils 3| and 32 which readily pass the lowfrequency signal currents. Large stopping capacity element 31 completesthe high frequency oscillator anode path to a point infrequency-determining circuit l3 of opposite phase to that of the besuppressed. However,

grid connection; A grid leak path extends from the central point of thesecondary winding of transformer l4 through high resistance element 38to the cathode. The device, accordingly, operates as two parallelconnected high frequency oscillators with their outputs differentiallyconnected to the load circuit 18. Accordingly, the unmodulated carrierfrequency component will whenever signals are incident upon microphonel6 one oscillator space circuit will prevail during the positive halfwave of the signal and the other during the reverse half wave so that apure modulated carrier wave will be supplied to load circuit I8.

In the circuit of Fig. 6, the oscillator and modulator have a pair ofanodes in common but the oscillator has a single impedance control gridwhile the modulator has two grids arranged in push-pull fashion. Theoscillator comprises the grid 3, anodes 8 and 9 connected in paralleland the frequency-determining circuit IS. The modulating input circuitis substantially identical with that of Fig. 1. The grid bias source forgrids 6 and 1 may be so poled as to polarize the grids normally eitherpositively or negatively with respect to the cathode as explained inconnection with the grid bias source of Fig. 2.

The circuit of Fig. 7 differs from the previously described circuits inits use of plate circuit modulation. Cathode 2, grid 3, anodes 8 and 9,plate current source 39 and frequency-determining circuit l3 comprisethe oscillation generator. The path connecting grid 3 to circuit l3 mayinclude the usual grid leak resistance and condenser combination. Thespace current path of the oscillator anodes may be traced by way ofcathode 2, space current source 39, the secondary winding of transformerl4 and the primary windings of the two output transformers 40 and 4|whose secondary windings are differentially connected to load circuitl8. In order to permit the anodes 8 and 9 to operate in parallel ingenerating high frequency oscillations, the oscillation frequencydetermining circuit I3 is connected by a lead 42 to the junction point43 of two capacity elements 44 connected between the leads extendingfrom the outer terminals of the secondary winding of transformer I4 tothe anodes. The capacity elements 44 transmit the high frequency not ofsuflicient capacity to appreciably shunt the speech or modulationfrequency currents impressed on its output circuit by the secondarywinding of transformer l4. Accordingly, the potentials of anodes 8 and 9alternately rise and fall in push-pull fashion in accordance with themodulating electromotive forces delivered by transformer l4. At the sametime the anodes undergo high frequency variations or potentialvariations for which they are eifeotively tied together electricallywith consequent simultaneous rise and fall of potential at theoscillation frequency. The oscillations deliveredby anode 8 and thosedelivered by anode 9 are accordingly modulated in the manner of thewell-known plate modulator circuit. During non-signaling intervals theanodes deliver equal amplitude unmodulated oscillations. Thedifferential circuit cone nection of transformers 43 and 4| causes theunmodulated equal amplitude cscillation to annul each others effect onload circuit l8 so that no unmodulated oscillations are transmittedthereto. Moreover, an instantaneous increase in oscillations deliveredby one anode is accompanied by a simultaneous decrease in theoscillations delivi but are a vered by the other.

the load circuit The differential connection makes these two changesadditive with respect to the output circuit |8. A capacity element 45 isconnected directly between the anodes 8 and 9 to reduce to a minimum anyhigh frequency oscillation difference of potential but is ofinsufficient capacity to permit a substantial diversion of modulationfrequency currents.

Fig. 8 discloses a circuit for generation and modulation of highfrequency oscillations by an electron discharge device in which thesignaling electromotive force controls a virtual cathode for the highfrequency carrier source. Referring to the drawings the device Iincludes the customary cathode 2, an impedance control electrode 46 anda foraminate anode 41. A source 48 of space current is connected betweenthe anode 41 and cathode 2. Microphone or other signal generatingelement |6, source l1 and primary winding of transformer |4 are includedin a circuit coupled by the transformer to the signal input control pathconnecting cathode 2 and grid 46 and which includes a grid biasingsource 49. A grid 5| positioned beyond the anode 41 is connected to thecathode by a loop circuit 52 tuned to the carrier oscillation frequencyand a grid leak path comprising capacity element 53 and high grid leakresistance 54. Oscillator anode 55 is connected to cathode 2 over a pathincluding a winding of three-winding transformer 56 and space currentsource 51. A second winding of transformer 56 constitutes part of theoscillation circuit 52 so that the anode circuit and the circuit of grid5| are coupled to generate sustained oscillations of a frequencysubstantially determined by the tuning of circuit 52. A third winding oftransformer 56 is connected to- |8 and serves to couple that circuit tothe oscillator output circuit. During the continuance of oscillations inloop circuit 52, the rectifying action of the grid leak circuit willcause grid 5| to be maintained at a negative potential, The entirecircuit of Fig. 8 is preferably so designed and adjusted that theresulting normal negative bias potential on grid 5| is sufiicient toretard electrons proceeding through the interstices of anode 41 beyondthe anode and to set up a virtual cathode 58 which serves as the cathodefor the oscillator. Since the number of electrons available at thevirtual cathode 58 is controlled by the electromotive forces impressedupon control grid 46, the oscillations generated which will vary inaccordance with the electron supply at 58 will, accordingly, beeffectively modulated by the speech or other signal or controlelectromotive force applied to grid 46. As a result, carrier frequencyoscillations will be supplied to load circuit l8 and whenever signalimpulses are impressed over transformer M, the carrier oscillationstransmitted to circuit |8 will be modulated by the signal impulses.

Fig. 9 illustrates a modification of the circuit of Fig. 8 according towhich the carrier oscillations are externally produced by a source 59and are impressed on the input circuit of high frequency control grid 5|by a transformer 60. The circuit of grid 5| includes a negative biassource 6| to assist in production of a virtual cathode. vIn otherrespects the elements correspond generally to those of Fig. 8 and aresimilarly designated. The operation of this circuit will, it isbelieved, be apparent without further description.

A harmonic generator or frequency multiplication circuit is illustratedin Fig. 10 in which an electron discharge device includes in thesequence of their position, a cathode 2, control grid 62,

- the proper potential,

foraminate anode 63, second'control grid 64, second foraminate anode 65,control grid 66 andmain anode 61. A space current source 68 is connectedbetween the cathode 2 and the anodes 63, 65 and 61. Grid 62 is suitablypolarized by grid biasing source 69. Grids 64 and 66 are so negativelybiased by sources 18 and 1| respectively, that virtual cathodes areproduced at 12 and 13. Grid leak and stopping condensers may be utilizedin the customary fashion instead of polarizing sources 69, 18 and 1|. Atuned circuit 14 is associated with the paths connecting grid 62 andanode 63 to the cathode 2 in such fashion that these three electrodesand their associated circuits and biasing sources constitute a source ofoscillations of a frequency f1 corresponding to the natural frequency ofcircuit 14. In similar fashion a tuned circuit is associated with grid64 and anode 65 cooperating with virtual cathode 12 to constitute asource of oscillations of frequency 1111 representing any desiredmultiple of the frequency f1 and corresponding to the tuning of thecircuit 15. A third circuit 16 tuned to the frequency lmh representingany desired harmonic of the oscillations produced in circuit 15 isassociated with the main anode 61, grid 66 and the virtual cathode 13 toproduce oscillations of the frequency of circuit 16. It will beapparent, therefore, that oscillations of the frequency f1 produced incircuit 14 give rise to a correspondingly pulsating source of electrons12 so that circuit 15 operates to produce oscillations of a multiplefrequency of those produced by circuit 14. In its turn circuit 15 andits associated electrodes set up at 13 a virtual source of electronspulsating at the multiple frequency corresponding to the tuning ofcircuit 15. In like manner, still higher frequency oscillations areproduced in the oscillator output circuit 16. Accordingly, the device asa whole comprises three oscillator stages, the first two of which eachserve to provide a virtual source of electrons of an oscillatingamplitude for the succeeding stage oscillator. Circuit 16 is coupled tothe load circuit It to supply the desired harmonic frequencyoscillations thereto.

Figs. 11 and 12 illustrate circuits for producing harmonics of afundamental frequency in which the elements nearer the cathode areconstructed and positioned to operate in push-pull fashion. In Fig. 11,for example, the cathode 2 is connected to tuned circuit 11 of frequencyis to which grids 18 and 19 are also connected at points differing 180in phase. Foraminate anodes 88 and 8| are connected to these samepoints, anode 88 being connected at a point of opposite phase withrespect to its cooperating grid 18 and anode 8| likewise being connectedto a point of opposite phase with respect to its cooperating grid 19.Space current source 82 is connected between the cathode 2 andtheforaminate anodes 88 and 8| and also between the cathode and theprincipal anode 83. A very large capacity condenser 84 in shunt tosource '82 provides a by-pass therearound for oscillations. Grid leakcircuits 65 and 85 serve to overcome the positive potential that wouldotherwise be impressed upon grids 18 and 19 by the source 82 and tocause the grids to be brought to with respect to the cathode.Ordinarily, although not necessarily, potentials of the two grids willbe somewhat negative with respect to that of the cathode. A tuned outputcircuit 81, preferably tuned to a harmonic njz of the frequency is, isincluded in series in the path between the cathode and the main anode83.

Fig. 12 comprises a primary oscillator including art.

cathode 2, tuned circuit", grids I8 and I9, foraminate anodes and 8|,space current source 82, by-pass capacity element 84 and grid leak paths85 and 99 corresponding to the similar elements of Fig. 11. Anadditional grid 89 between the anodes 80 and 8! and the main anode 90 isbiased negatively with respect to the cathode by means of source 9| soas to produce a virtual source 92 of electrons between the foraminateanodes and the grid 09. In the external circuit of the grid, 89 is atuned loop circuit 93 which is preferably tuned to multiple nfs of thefrequency of the primary oscillations. The circuit 93 is coupled to theexternal circuit of anode 99 to provide the necessary feed-back forproduction of the multiple frequency oscillation by a threewindingtransformer 94, the third winding of which is included in series withthe load circuit I8 to transfer harmonic frequency oscillations of thefrequency nfz thereto.

Fig. 13 illustrates a circuit for producing high power or harmonicoscillations from a crystal controlled circuit. The primary oscillatorcomprises an electron discharge device having a cathode 2, a controlgrid 3 and a foraminate anode 4. A loop 95 tuned to the frequency ofoscillations to be produced is included in the anode circuit. The gridcircuit includes piezoelectric element 96 of any well-known type shuntedby leak resistance 97. The element 96 is designed and constructed inaccordance with well-known piezoelectric technique to be resonant atsubstantially the desired oscillation frequency. Accordingly, theprimary oscillator, as so far described, will produce oscillations, thefrequency of which is substantially determined by the natural period ofvibration of the piezoelectric device 96, in the circuit 95 tuned toapproximately the same frequency in accordance with well-known practice.The electron discharge device also includes a main anode 98, a grid 99cooperating therewith and a screen grid I00 interposed between theforaminate anode 4 and electrodes 98 and 99. Grid I00 is preferablypolarized by a source IOI to such a potential as to produce or assist inproducing a virtual source of electrons I02 in the region beyond anode4. It will be understood however as indicated in the drawings anddescribed in connection with Fig. 2, the grid bias source I 0| mayrender grid I00 either normally positive or negative with respect to thecathode. Aspace current source I03 serves to positively polarize themain anode 98 as well as the foraminate anode 4. This source will bedesigned to impress an unusually large potential upon anode 98 when highpower is desired. By-pass capacity elements I04 and I05 havingnegligible reactance at the oscillation frequencies involved areassociated with the space current source I03 in the manner indicated inthe drawings. A tuned loop I06 is connected with the main anode 98 andthe grid 99 to regeneratively couple their respective circuits wherebythe apparatus tends to produce oscillations of the resonance frequencyof circuit I06. A grid leak resistance I0! and shunting grid leakcondenser I08 in the circuit of grid 99 normally maintain the grid 99 ata negative potential during the occurrence of oscillations in circuitI06 in a manner well understood in the If it is desired to transmitoscillations of the fundamental frequency to the load circuit I8, thecircuit I06 coupled thereto will be tuned to the frequency of theprimary oscillator. If, however, it is desired to supply to the loadcircuit I8 harmonic oscillations of the primary oscillation frequency,the circuit I06 will be tuned to the desired harmonic frequency. In thatevent the screen grid I99 may be omitted if it is desired to simplifythe apparatus, although it is preferable to employ it.

Fig. 14 shows another circuit for an oscillator for producing high poweroscillations employing the virtual cathode principle. As shown, thedischarge device I includes a cathode 2, control grid 3, a positivelypolarized screen I99, an oscillator grid H0 and an oscillator anode III.Connected between cathode 2 and grid 3 are piezoelectric element 96 andshunting leak resistance 97. A tuned loop H2 is connected between thegrid I I0 and anode I I I, the connection to the grid passing by Way oflarge capacity element H3. A path from the cathode 2 leads by way ofspace current source H4 and large by-pass condenser I I5 to a centralpoint in the inductance of the tuned loop H2, A grid leak resistance II6 connects grid H0 to cathode 2 thus permitting grid H0 to be normallynegatively polarized by grid rectification action during continuance ofoscillations in the circuit H2. The negative polarization of grid H0 ispreferably sufiicient so that in cooperation with the other elements itproduces a' virtual source of electrons at H! in the region between thescreen I09 and the grid H0. A coupling capacity element H8 of smallcapacity connects the piezoelectric device 96 to the oscillation circuitH2 to permit the reactance of the device 36 to control the frequency ofthe oscillations generated. It will be understood that in operationelectrons are drawn to the positively polarized screen I09 which is ineffect an auxiliary anode operating at a reduced anode voltage by virtueof the tap I I9 which connects the external terminal of the element I09to the space current source I I 4. The virtual cathode H1 accordinglyprovides electrons in pulsations of a frequency determined by thepiezoelectric element 96. Accordingly, the virtual cathode HIcooperating with the grid H0 and the anode III with the relatively highpotential source. H4 serves to produce oscillations of high power in thecircuit II 2. Circuit I I2 is tuned in the usual manner to substantiallythe natural frequency vibration of piezoelectric element 96 and iscoupled to load circuit I8 to supply high power oscillations thereto.

In the various figures of the drawings the load circuit I8 should beunderstood as representative of any. suitable transmission path. Forexample, it may be a carrier wave transmission line or it may be acircuit leading to an antenna.

The principles of the invention are, in general, applicable todemodulators as well as to modulators. In general, therefore, the sourceof low frequency modulating signals may be replaced by a high frequencyincoming transmission line or by a connection from a receiving antenna.It will be understood that in all such instances, it will be necessaryto provide the incoming path with a suitable high frequency transformerand that it will be necessary to eliminate from that path impedanceelements which would interfere with effective transmission of theincoming high frequency waves. 7

For the purpose of simplifying the drawings, unidirectional sources ofspace current and polarizing electromotive forces have been illustratedand the discharge devices have been disclosed as of the thermioniccathode type. It will, of course, be understood that any suitable sourceof rectified current may be employed in a wellknown manner for currentsupply purposes and that the discharge devices may be of the indirectlyheated cathode type. It will, of course, also be understood that by-passcondensers are to be connected across any current or potential supplysource where impedance through the source, or in lead wires to thesource, are appreciable and that such current or potential supplysources are not restricted to the specific locations indicated, but maybe shifted to other positions according to well-known practices in theart. It will also be understood that potential biases for gridelectrodes may be either primary current sources or grid leak andstopping condenser combinations, or both, in all oscillator grid circuitpaths wherever a grid bias or grid leak stopping condenser combinationis shown.

What is claimed is:

1. Electron discharge apparatus including a cathode, an impedancecontrol element and a screen form anode, means for polarizing theimpedance control element and the anode to constitute a virtual sourceof electrons in the space beyond the anode, a pair of coplanar controlgrids, a pair of coplanar anodes, the pair of grids lying respectivelyin the paths of electrons passing from the virtual source to the pair ofanodes and an output circuit connected to the coplanar anodes.

2. A modulation apparatus comprising an electron discharge device havingthree electrodes including a cathode and two foraminate electrodes,means for polarizing one of the foraminate electrodes to cause it toserve as an anode, external paths connecting each of the foraminateelectrodes to the cathode, means for coupling the external paths tocause oscillations to be produced.

a pair of coplanar modulating grids and a pair of coplanar anodesincluded within the device, means for impressing modulatingelectromotive forces in push-pull fashion between the coplanar grids,and a path connecting the coplanar anodes and including means forderiving modulated currents therefrom.

3. A modulating device comprising an electron discharge container, acathode, an impedance control element and an anode therein constitutingwith their external circuits an oscillator, a second control electrodeand two output electrodes in said container, an output circuit connectedto the two output electrodes and a modulation control circuit connectedto the second control electrode, and means whereby the output circuit inresponse to signal electromotive forces applied to the modulationcontrol circuit may yield oscillations modulated in accordance with thesignal electromotive forces and substantially free from an unmodulatedcarrier frequency component.

4. A modulator comprising an electron discharge device having cathode,grid and a pair of screen form anodes, means for impressing carrierfrequency oscillations between the grid and cathode, a pair of mainanodes in the space beyond the screen anodes, a modulating circuitconnected between the screen anodes for impressing modulatedelectromotive forces therebetween and an output circuit connectedbetween the cathode and the pair of main anodes for deriving modulatedcarrier frequency oscillation therefrom.

5. An electron discharge device having a oath-- ode, a grid and aperforated anode, external coupled grid-cathode andanode-cathodercircuits to produce oscillations and project electrons inpulsating fashion through the perforated anode, a

modulating means and. a pair of anodes located in the path of theprojected electrons, an ex ternal output circuit differentiallyconnected between anodes of the pair and a source of modulatingelectromotive force connected to the modulating means wherebyoscillations may be derived from the output circuit having frequenciesof the sum and difference respectively of the frequency of theoscillations and the frequency of the modulating electromotive forcefree from unmodulated components of the oscillation frequency.

6. In combination, an electron discharge device having a cathode, agrid, an anode, external anode-cathode and grid-cathode circuits coupledto each other to cause the device to produce oscillations, the anodeconsisting of two separate foraminate parts to permit some of theelectrons impelled theretoward to pass put anodes positioned in the lineof the electrons passing through the foraminate anodes, a low frequencymodulating signal circuit connected in push-pull relation to theforaminate anodes and a load circuit differentially connected to theoutput anodes.

7. A system for producing modulated oscillations comprising an electrondischarge device having a cathode, a grid and two coplanar anodes, asource of space current connected between the cathode and anodes, aresonant circuit connected to the cathode, the grid, and the anodes insuch fashion as to constitute an oscillator in which the anodes operatein parallel with respect to the space current source, a source ofmodulating currents, means for connecting said source of modulatingcurrents in push-pull relation to the two anodes, a load circuit, andmeans for connecting the two anodes in differential fashion to the loadcircuit whereby the oscillations delivered thereto are substantiallyfree from an unmodulated component.

8. A system for transmitting modulated carrier waves comprising anelectron discharge device having a. cathode, a grid and a foraminateanode, a path including a. polarizing source connecting the cathode andforaminate anode, a circuit connected between the grid and cathode andincluding means for impressing carrier frequency signal. waves thereon,a pair of output anodes in position to receive electrons projectedthrough the foraminate anode, a modulating grid in the path of theprojected electrons, means for impressing audio frequency potentialsupon the modulating grid with respect to the cathode; an

output circuit connected differentially between the two output anodesand the cathode and a load circuit coupled thereto to receive signalmodulated carrier frequency oscillations therefrom.

9. An electron discharge device comprising a cathode, a grid and aforaminate anode, an output anode lying in the path of electronsprojected through the foraminate anode, means also lying in that pathfor producing a virtual cathode in the region between the foraminateanode and the output anode, a carrier frequency input circuit connectingthe grid and the cathode, a path including a polarizing sourceconnecting the foraminate anode and the cathode, means for controllingthe impedance of the device between the virtual cathode and the outputanode in accordance with audio frequency electromotive forces, aresonant loop circuit connected between the anode and the cathode, awork circuit associated with the resonant loop circuit, and means forpreventing the output anode from impressing untherethrough, outcathode,a path including polarizing means connecting the anode to the cathode,the electron discharge device also including a second control electrodeand two coplanar output electrodes, an output circuit differentiallyconnected to the two output electrodes and the cathode, and a modulationcontrol circuit connected between the second control electrode and thecathode whereby the output circuit in response to modulation frequencyelectromotive forces applied to the second control element may yieldmodulated carrier frequency oscillations substantially free from anunmodulated carrier frequency component.

11. A system for producing modulated carrier oscillations comprising anelectron discharge device having electron discharge electrodes and animpedance control element, external circuits connected to the electrodesand the element and so coupled as to cause the device to produce astream of electrons having a periodic variation in its amplitude, a pairof output anodes symmetrically positioned with respect to the varyingamplitude electron stream, means for differentially controlling theportions of the stream of electrons reaching each anode in accordancewith signals, and an output circuit connected between the output anodeswhereby modulated carrier frequency oscillations are delivered to theoutput circuit free from an unmodulated component.

12. A sysmm for intermodulating two sets of different frequencyoscillations, comprising an electron discharge device having electrondischarge electrodes including a cathode and anode means to receiveelectrons therefrom, an impedance control element, external circuitsconnected to the electrodes and to the element and so coupled as tocause the device to produce a stream of electrons having a periodicvariation in its amplitude corresponding to one set of the oscillationsto be intermodulated, a second anode means positioned in the path of thevarying amplitude electron stream and polarized positively to receiveelectrons. therefrom, the anode means nearer the cathode beingforaminate to permit passage therethrough of electrons to the otheranode means, one of the anode means consisting of two separate partspositioned symmetrically with respect to the electron stream and betweenwhich the electron stream is divided, and means for controlling theimpedance presented to the two parts of the stream in accordance with aset of oscillations of the other frequency.

13. A system for producing oscillations comprising an electric dischargedevice having a cathode, fcraminate anode means, a second anode means ingeneral alignment with the cathode and the foraminate means and moreremote from the cathode than the foraminate means, a source ofelectromotive force connected in circuit between the cathode and theforaminate anode means to impel a beam of electrons from the cathode,impedance control means located in the space traversed by the electronbeam, intercoupled external connections, including impedance controlpolarizing means, from said cathode to said impedance control means andsaid foraminate anode means whereby oscillations are produced, one ofthe anode means consisting of two separate parts symmetricallypositioned with respect to the electron beam emanating from the cathodeand between which that anode beam is divided, the other anode meansencompassing substantially the entire beam, and a load circuit and asource of anode potential connected between the second anode means andthe cathode.

14. An oscillation producing system comprising an electric dischargedevice having a cathode, a

first anode means consisting of a pair of elements closely adjacent tobut electrically insulated from each other and with their principalelectron re ceiving surfaces lying generally in the same plane, the twoelements being positioned symmetrically with respect to a line from thecathode perpendicular to said plane and serving when positivelypolarized to develop a pair of contiguous electron streams from thecathode, circuits including polarizing means connecting the pair ofanode elements in push pull fashion to the cathode, impedance controlmeans positioned adjacent each stream, a second anode means and a secondimpedance control means each encompassing an area through which both ofthe contiguous electron streams pass, one of said anode means beingforaminate to permit passage of the electron streams to the other anodemeans, means for polarizing the second anode means with respect to thecathode, electrical connections to the cathode for one of the anodemeans and its associated impedance control means so coupled as to causethe production of oscillations, and means for applying an alternatingelectromotive force to the other impedance control means to modulateboth the electron streams in accordance with the applied electromotiveforce.

15. A system for production and modification of electrical oscillationscomprising an electric discharge device including a cathode, foraminateanode means, a grid, circuits connecting the cathode to the grid andanode means and including polarizing means whereby oscillations areproduced, means for reducing the velocity of electrons which pass theforaminate anode means to constitute a virtual cathode, two coldelectrodes beyond the virtual cathode in the path of the electrons whichpass through the foraminate anode means, a closed tuned loop circuitcomprising an inductance element and a capacity element having the twocommon connected respectively to the two cold electrodes, a connectionfrom a central point in one of the elements to the cathode, and anenergy transmission circuit connected in energy transfer relation to thetuned loop circuit.

16. In an oscillation producing and modifying system, an electricdischarge device comprising a cathode, anode means, impedance controlmeans, connections including polarizing means from the anode means andthe impedance control means to the cathode, a second anode means, asecond impedance control means, connections including polarizing meansfrom the second anode means and the second impedance control means tothe cathode, one set of anode means and impedance control means beingforaminate and the other lying in the path of the same electron streamfrom the cathode so that the electron emission from the cathode iscontrolled by both, the circuits connecting one set of anode means andimpedance control means to the cathode terminals of the elements beingintercoupled to constitute an oscillator, one anode means comprising twoinsulated anode elements equidistant from the cathode and symmetricallyplaced with respect to the total electron stream so as to divide thetotal electron stream into two streams, and means including theimpedance control means associated therewith for controlling theirrespective streams with the same controlling electromotive force.

17,. An oscillation producing and transmitting system comprising anelectric discharge device having a cathode, a set of two foraminate coldelectrodes lying at different distances from and in the samedirection'from the cathode and externally connected thereto, means forrendering one of the electrodes positive with respect to the cathode tocause a stream of electrons to be impelled toward it 'from the cathode,means for setting up such an electric field in the region beyond thecold electrodes as to retard electrons and constitute a virtual cathode,a second set of two cold electrodes both lying in the zone of theelectron stream and beyond the virtual cathode, means for positivelypolarizing at least one of the electrodes of the second set with respectto the cathode, external paths connecting the electrodes of the secondset to the cathode and each including at least a portion of a closedloop tuned circuit electrically coupling the paths, and means controlledby the current in the external path from the cathode to one of thepositively polarized electrodes for causing one of the other coldelectrodes to present an impedance to the electron stream proceeding tosaid positively polarized electrode which varies at the frequency of theoscillations which it is desired to produce, whereby oscillations areproduced and corresponding oscillations are supplied from the second setof cold electrodes to the closed loop tuned circuit.

RAYMOND A. HEISING.

